In recent years, by the utilization of their outstanding features such as slim body and low power consumption, liquid crystal display devices have been widely applied to various devices including information devices, such as notebook personal computers, mobile phones, electronic organizers, etc., and camcorders which have a liquid crystal monitor. The VA (Vertical Alignment) mode has been proposed as a display mode which is capable of realizing a higher contrast and a wider viewing angle in the liquid crystal display devices. The VA mode has been employed in many liquid crystal display devices nowadays. The VA mode liquid crystal display devices include a vertical alignment liquid crystal layer in which liquid crystal molecules are oriented generally vertical to the substrate surface in the absence of an applied voltage.
A known one of the VA mode is MVA (Multi-domain Vertical Alignment) mode (for example, Patent Document 1). In the MVA mode, a pair of substrates which oppose each other via a liquid crystal layer are each provided with an alignment controlling structure which is configured to control the alignment of the liquid crystal molecules. The alignment controlling structure is, specifically, a protrusion which is made of a dielectric substance or a slit which is formed in an electrode. When the alignment controlling structure such as a protrusion or a slit is provided, a plurality of regions among which the azimuth of inclination of the liquid crystal molecules is different (referred to as “liquid crystal domains”) are formed in the presence of an applied voltage across the liquid crystal layer. Therefore, the azimuthal angle dependence of the display characteristics is ameliorated, and the viewing angle characteristics are improved.
Although, in the VA mode liquid crystal display devices, display of wide viewing angles and high quality is realized as described above, there is a problem about the viewing angle characteristics which has been recently growing. Specifically, the problem is the difference between the γ characteristic that is obtained when viewed from the front and the γ characteristic that is obtained when obliquely viewed, i.e., the viewing angle dependence of the γ characteristic. The γ characteristic refers to the grayscale dependence of the display luminance. When the γ characteristic is different between the front viewing direction and the oblique viewing direction, the grayscale display state varies according to the viewing direction, resulting in display with a sense of incongruity.
The viewing angle dependence of the γ characteristic in the VA mode (which is also referred to as “γ shift”) is perceived as such a phenomenon that the display luminance which is detected when obliquely viewed is higher than the display luminance which is supposed to be detected (which is called a “whitening” phenomenon). If the whitening phenomenon occurs, such a problem also occurs that the color which is rendered by a pixel when viewed from an oblique direction is different from the color which is rendered by the pixel when viewed from the front direction.
As the technique for reduction of the γ shift (whitening phenomenon), a technique called “multi-pixel driving” has been proposed (for example, Patent Documents 2 and 3). According to this technique, one pixel is divided into a plurality of sub-pixels (typically, two sub-pixels) which provide different luminances. Specifically, one pixel electrode is divided into a plurality of sub-pixel electrodes (typically, two sub-pixel electrodes) which are electrically independent of each other. Potentials which are different from each other are applied to the respective sub-pixel electrodes such that the effective voltages that are applied across the liquid crystal layers of the respective sub-pixels can be different from each other.
For example, a plurality of TFTs which are coupled to different signal lines are provided in each pixel, and respective ones of the plurality of sub-pixel electrodes are coupled to respective ones of the plurality of TFTs. This arrangement enables supply of different signal voltages (grayscale voltages) to the respective sub-pixel electrodes. Alternatively, the storage capacitance counter electrodes that form the storage capacitances in respective sub-pixels are configured to be electrically independent, and different CS voltages are supplied from storage capacitance lines to the respective storage capacitance counter electrodes. This arrangement enables supply of different potentials to the respective sub-pixel electrodes by means of division of capacitance. When each pixel is divided into a plurality of sub-pixels which provide different luminances, the display is observed in which different γ characteristics are in a mixed state, so that the γ shift is reduced.
Another one of the VA mode which is widely known is CPA (Continuous Pinwheel Alignment) mode (for example, Patent Documents 4 and 5). In the CPA mode, an opening or notch is formed in the pixel electrode such that the pixel electrode is divided into a plurality of regions (which are referred to as “unit solid portions”). An oblique electric field produced at the edge of the opening or notch is used to realize a radial inclination alignment (axially-symmetric alignment) of the liquid crystal molecules, whereby a wide viewing angle is achieved. Also, a protrusion or opening is formed in the counter electrode such that the center axis of the liquid crystal domains that are in the radial inclination alignment is fixed, whereby the stability of the radial inclination alignment is further improved.
When a configuration which utilizes linearly-polarized light, i.e., a configuration where display is realized by allowing linearly-polarized light to enter the liquid crystal layer such that the linearly-polarized light is modulated, is employed in the CPA mode, the transmittance decreases. This is because, in the CPA mode, the liquid crystal molecules are oriented in substantially all azimuths in the presence of an applied voltage, and therefore, liquid crystal molecules which are oriented in an azimuth generally parallel to or an azimuth generally perpendicular to the polarization direction of linearly-polarized light that enters the liquid crystal layer do not contribute to the transmittance.
On the other hand, when a configuration which utilizes circularly-polarized light, i.e., a configuration where display is realized by allowing circularly-polarized light to enter the liquid crystal layer such that the circularly-polarized light is modulated, is employed in the CPA mode, all of liquid crystal molecules which are inclined in the presence of an applied voltage contribute to the transmittance. Therefore, the decrease of the transmittance can be prevented, and bright display can be realized.